diff --git a/lib/attribute.js b/lib/attribute.js
index 4881c3d..02be8a5 100644
--- a/lib/attribute.js
+++ b/lib/attribute.js
@@ -76,7 +76,7 @@ function Attribute(options) {
     };
   });
 
-  if (options.vals !== undefined)
+  if (options.vals !== undefined && options.vals !== null)
     this.vals = options.vals;
 
 }